In wireless communication, a signal transmitted from a transmitting antenna arrives at a receiving antenna through a plurality of routes. Signals having traveled through these routes of varying lengths are combined in a state these signals have different signal powers and phases, and the demodulation performance of the receiving apparatus is deteriorated. Consequently, in order to demodulate a signal correctly in the receiving apparatus, channel estimation is an important technology.
Generally, channel estimation is performed as follows: First, a channel estimation sequence (CES) is transmitted from the transmitting side to the receiving side. The receiving side prepares a known signal sequence that is the same as the channel estimation sequence transmitted from the transmitting side, and finds the correlation between that known signal sequence and a sequence detected by way of detection from a received signal.
In channel estimation, generally, coherent detection is used for the detection scheme. Next, from the correlation results obtained, positions where sharp peaks appear are detected as the times of arrival of the direct wave and delayed waves, and the amount of signal propagation delay is estimated. Consequently, in channel estimation, a signal sequence having a good autocorrelation characteristic is used as a channel estimation sequence. Then, based on the amount of propagation delay estimated, the magnitude of amplitude fluctuation due to inter-symbol interference is found, and an amplitude coefficient is detected.
For example, patent literature 1 discloses a method of improving the accuracy of channel estimation. With the method disclosed in patent literature 1, the receiving side receives a known signal sequence transmitted from a communicating party and finds a power delay profile by complex correlation processing of the known signal sequence and a received signal sequence. Then, the arrival time and magnitude of the direct wave component is detected from the delay profile, and a replica of the correlation value of the direct wave is generated. Next, the generated replica is subtracted from the delay profile (i.e. correlation results), so that the accuracy of estimation of the arrival time of delayed waves is improved. The method disclosed in patent literature 1 is premised on the use of coherent detection as the detection scheme.